Disc drive recorders for use in data recording systems comprise, in general, combinations of read/write heads and rotating magnetic discs which interact for the recording of data on a magnetic surface of each disc. The discs usually are assembled in a stacked configuration referred to as disc packs in a manner to be removably set onto the disc drive to thereafter be rotated for movement past the heads. The read/write heads are mounted on a carriage assembly for movement into proximity with the disc surfaces and translation across the disc surfaces so as to read and record data in concentric circles on the disc magnetic surface. The data is recorded by a magnetic interaction between the heads and the magnetic material fixed to the disc.
In the past, the read/write heads, usually one for each disc surface, have been actuated along a straight line across the disc surface. A linear motor positioned to one side of the disc has been utilized to shift a roller bearing supported carriage along a straight line coinciding with a radius of the discs. In this manner the complete head support assembly and heads are all moved an equal distance as translation of the heads across the disc surface is accomplished. While there are certain well recognized advantages to such a head positioning apparatus, one disadvantage involves the inertia which must be overcome to move the heads from position to position.
There now has been developed a method of positioning the heads whereby the head arm assemblies are rotated about a fixed point in a manner to move the heads along an arcuate path across the disc surface. In this apparatus the heads are supported on the distal ends of horizontally extending arms having the opposite end fixed to an assembly mounted for rotation about a vertical axis. By rotation of the arms about an axis spaced from the discs, the heads are moved along an arcuate path roughly intersecting the center point of the discs for reading and writing information on the disc surfaces. Thus the heads are moved about the maximum radius of the apparatus so that higher acceleration can be gained for a quick access to the various track positions on the disc surface. Additionally, the head end of the arms presents less inertial resistance to movement thereby further permitting rapid acceleration between positions.
For positioning of the heads, there is utilized a rotary motor fixed to the rotatable assembly preferably at the axis of rotation which motor, upon energization, moves the heads into and out of proximity to the discs and to various positions spaced across the disc surfaces. The actuator itself varies from the linear actuator previously used in that the armature or rotor generally remains in a constant air gap such that a constant force can be exerted thereon for movement of the heads.
With the realization that the heads can be successfully moved by a rotary mechanism for positioning at the disc surface, it naturally follows that a plurality of head arm assemblies can be moved by the same rotary actuator. Such is not the case with the linear actuator since even if an additional head arm assembly was positioned at the other end of the linear actuator the heads thereon would be moved away from the disc pack while the other set was moved toward the disc pack. In the case of the rotary actuator the rotating discs are positioned at equal distances about the actuator such that each of the read/write heads enter the disc pack area from the same side. Thereafter when all of the heads are moved out of proximity with the disc pack, the disc packs can be removed in the normal manner. As one advantage gained by such an apparatus, the heads address a plurality of data cylinders (data locations on each disc vertically coinciding on one disc pack) at any one positioning of the actuator thereby making more data locations "on-line" for reading and recording of data. Further for the cost of only a single actuator a plurality of disc packs are addressed thereby providing less complicated and hopefully a more economical disc drive.
However, one problem remains which is not present in the linear actuated disc drives. This problem involves the need for loading and unloading the heads as they are moved to a position near the disc surfaces. With the linear actuator, the heads are loaded automatically as they are moved into alignment with the discs by a camming action resulting from interacting surfaces on the supporting arms and a stationary structure on the disc drive. The camming occurs automatically as the heads are moved toward the discs. Since only one head support assembly is utilized per each disc pack and actuator, it is sufficient to utilize the linear movement of the head support assembly for loading and unloading the heads. However with the utilization of rotary actuators, and particularly where a plurality of disc packs are used with one actuator, there has developed a need for unloading one set of heads possibly while continuing actuation of heads associated with another disc pack. This need arises for many reasons, not the least of which involves the possibility that disc packs may not be assembled at all positions thereby requiring the heads at the location where a disc pack is not mounted to be maintained unloaded while permitting the positioning of the heads at the other locations where a disc pack is in position. Thus the present invention is directed to the providing of head loading and unloading apparatus which can be used with rotary actuated heads with particular application in disc drives utilizing a plurality of sets of rotary actuated heads cooperating with a plurality of disc packs.